FIG. 1 is a cross-sectional view of a related art sound transducer.
As illustrated in FIG. 1, a general sound transducer (speaker) includes a frame 1, a yoke 2 insertedly installed within the frame 1, an inner magnet 3 and an outer magnet 4 transmitting magnetic flux to the yoke 2 or receiving magnetic flux from the yoke 2, respectively, an inner top plate 5 and an outer top plate 6 receiving magnetic flux from the inner magnet 3 or the outer magnet 4 and transmitting magnetic flux to a voice coil 7 at a right angle, respectively, the voice coil 7 having a portion inserted in a gap between the inner magnet 3 and the inner top plate 5 and the outer magnet 5 and the outer top plate 6, a vibration plate 8 having the voice coil 7 attached to an inner side thereof and generating vibrations according to a vertical movement of the voice coil 7, a projector 10 having a sound discharge hole 11 and protecting the vibration plate 8, and the like.
FIG. 2 is a schematic view of an enclosure in which the sound transducer is installed. As illustrated in FIG. 2, the related art sound transducer is insertedly installed in a space of an enclosure case 15. A draft hole 16 is formed on a lateral surface of the frame 1 in a longer-axis direction, and thus, when the sound transducer is inserted in the enclosure case 16, the draft hole 16 is in contact with a lateral surface of the case 15 and closed, restraining a smooth air flow. In this manner, the draft hole 16 of the related art sound transducer is formed in the longer side of the frame or in the vicinity of the center of a cross-section of the frame 1.
In the case of the structure, a size (or a sectional area) of a magnetic circuit based on the yoke 2 and the outer magnet 4 is required to be reduced due to the formation position of the draft hole 16.